1. Field of the Invention
This invention relates to a bonding structure involving bonding wires connected to bonding pads. More particularly, the invention relates to the bonding structure which is preferred for application to an actuator device equipped with a vibration plate and a piezoelectric element, especially, for application to a liquid-jet head where a portion of a pressure generating chamber communicating with a nozzle orifice for ejecting ink droplets is constituted of a vibration plate, a piezoelectric element is formed on the surface of the vibration plate, and ink droplets are ejected by displacement of a piezoelectric layer.
2. Description of the Related Art
An actuator device equipped with a piezoelectric element displaced by application of a voltage is installed, for example, on a liquid-jet head for jetting liquid droplets. Known as such a liquid-jet head is, for example, an ink-jet recording head in which a portion of a pressure generating chamber communicating with a nozzle orifice is constituted of a vibration plate, and the vibration plate is deformed by a piezoelectric element to pressurize ink in the pressure generating chamber, thereby ejecting ink droplets from the nozzle orifice. Two types of ink-jet recording heads are put into practical use. One of them is mounted with a piezoelectric actuator device of longitudinal vibration mode which expands and contracts in the axial direction of the piezoelectric element. The other is mounted with a piezoelectric actuator device of flexural vibration mode.
The latter ink-jet recording head adopts a structure in which a drive IC is installed on a plate bonded to a passage-forming substrate having the pressure generating chamber formed therein, for example, a reservoir forming plate, and the drive IC and a terminal portion of a lead electrode leading from each piezoelectric element are electrically connected together by a bonding wire by means of wire bonding (see, for example, Japanese Patent Application Laid-Open No. 2002-160366 (page 3, FIG. 2)). Wire bonding, which is performed in the production of such an ink-jet recording head, is carried out by connecting one end of a bonding wire to a terminal portion of the drive IC with the use of a capillary, and then connecting the other end of the bonding wire to a bonding pad which is a terminal portion of the lead electrode.
With the ink-jet recording head, it is attempted to downsize mounted components, and arrange the vibrators at high density. A high density is also demanded of wiring for a device using a bonding wire. In mounting a bonding wire obliquely, it is preferred to arrange the bonding wire at a large angle in order to downsize the component. From the viewpoint of high density mounting of the vibrators as well, it is preferred to decrease the pitch of the bonding wires for an increased density.
Thus, techniques for applying the bonding wire obliquely to achieve downsizing have hitherto been known (for example, Japanese Patent Application Laid-Open No. 2003-31610 (FIGS. 1, 4 and 5)). The conventional techniques, however, have not defined optimum pitch or angle, and it is desired that the optimal status of arrangement be specified. According to the conventional technologies, moreover, a narrow pitch is achieved by arranging the points of bonding zigzag to prevent contact with the adjacent wire. However, the points of bonding should preferably be arranged on a straight line in consideration of the downsizing of mounted components.
The above-described problems are true of not only liquid-jet heads such as ink-jet recording heads, but also devices having a bonding wire connecting structure using semiconductor elements such as LSI and IC.